1. Technical Field
The present disclosure relates to a negative electrode active material for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery.
2. Related Art
A lithium ion secondary battery is lighter in weight and has higher capacity than a nickel-cadmium battery, a nickel hydride battery, and the like. Thus, lithium ion secondary batteries are widely used as a power supply for portable electronic devices. The lithium ion secondary battery is also a strong candidate for a power supply mounted on hybrid automobiles or electric automobiles. With the decrease in size and increase in functionality of portable electronic devices in recent years, the lithium ion secondary battery used for the power supply is expected to have higher capacity.
The capacity of the lithium ion secondary battery is mainly dependent on an electrode active material. Generally, as a negative electrode active material, graphite is utilized. However, the theoretical capacity of graphite is 372 mAh/g, and a battery with capacity of approximately 350 mAh/g is already put to practical use. In order to obtain a nonaqueous electrolyte secondary battery having sufficient capacity as an energy source for future high-functionality portable devices, even higher capacity needs to be provided. For this purpose, a negative electrode material with greater theoretical capacity than that of graphite is necessary.
An example of such negative electrode active material is a composition containing an iron oxide (oxide containing iron as a constituent element), such as Fe2O3. The iron oxide is capable of electrochemical adsorption and desorption of lithium ions, and is also capable of charging and discharging of much higher capacity than graphite. In particular, the theoretical discharge capacity of Fe2O3 is 1005 mAh/g. Namely, Fe2O3 is known to have 2.7 times as high as that of graphite (JOURNAL OF SOLID STATE CHEMISTRY 55, 280-286 (1984); Adv. Funct. Mater. 2007, 17, 2792-2799; and Journal of Power Sources 178 (2008) 402-408).